1. Technical Field
The present invention relates to a gear device having an inner-tooth pin inside an outer cylinder.
2. Background
As an eccentric oscillating gear device for driving a robot member or the like, as described in Japanese Patent No. 5779120, there is known a gear device that has an inner-tooth gear and an outer-tooth gear and extracts relative rotation between the inner-tooth gear and the outer-tooth gear as relative rotation between a carrier and a casing. This inner-tooth gear has a cylindrical casing, an outer pin supported in a pin groove formed on an inner peripheral surface of said casing and thus constituting an inner tooth, a pair of retaining rings that restrict movement of the outer pin in an axial direction, and a restriction member interposed between the retaining rings and the outer pin.
On the inner peripheral surface of the cylindrical casing, concave portions are formed on both sides of the pin groove in the axial direction, respectively. With the outer pin fitted into the pin groove, by the pair of retaining rings latched to the concave portions, respectively, movement of the outer pin in the axial direction is restricted via the above-described restriction member.
In the above-described eccentric oscillating gear device, in order to mount the pair of retaining rings for restricting movement of the outer pin in the axial direction, work is required to fit said pair of retaining rings into the concave portions formed on the inner peripheral surface of the casing, leading to a problem that assembling workability is hardly improved.